Glass has been widely used as a substrate for a display device such as a liquid crystal display device and an organic EL display device, a substrate for a color filter, a substrate for a solar cell, and the like. In recent years, however, a plastic material is being considered as a substitute for a glass substrate owing to such reasons that the glass substrate is liable to fracture, cannot be bent, is not suitable for reduction in weight due to the large specific gravity thereof, and the like. For example, substrates made of thermoplastic resin such as polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyolefin and polyethersulfone are proposed (for example, in JP-A-2007-268711, Patent Document 1).
However, these conventional plastic materials for substituting for glass experienced thermal deformation in some cases when it was maintained at a high temperature or subjected to heat treatment. As a method for suppressing thermal deformation, a method of laminating an inorganic fine particle layer on at least one side of a resin film has been proposed (e.g. JP-A-2006-347054; Patent Document 2).
The thermal deformation described in Examples of Patent Document 2 indicates thermal contraction/thermal expansion, which occurs in a temperature range of 100° C. or lower. If the temperature is above the range, it is highly likely that a product is thermally expanded to a greater extent since the temperature reaches the glass transition temperature. Since the heatproof temperature of 200° C. or higher is required for the recent film for a display device substrate, the conventional production method cannot avoid thermal contraction/thermal expansion or deformation such as warpage.
On the other hand, a conventional method for producing a curable resin film is a method of applying a liquid curable resin composition onto a substrate film and, after drying by heating when the composition contains a solvent, curing the composition by heating and/or light irradiation. However, a conventional method as described above makes a slight difference in the contraction degree upon heating between the substrate side and the surface side of the layer of the curable resin composition. Due to the difference, deformation such as warpage occurs upon heating/cooling.